In Search of Microscopic Evidence for Molecular Level Negative Thermal Expansion in Fullerenes

F. Cimpoesu; H. Takagi; J. Cao; J. L. Musfeldt; N. Dragoe; R. J. Cross; S. Brown; S. Ito

REVIEW

In Search of Microscopic Evidence for Molecular Level Negative Thermal Expansion in Fullerenes

S. Brown, J. Cao, J. L. Musfeldt, N. Dragoe, F. Cimpoesu, S. Ito, H. Takagi, R. J. Cross

Materials Science · Submitted 22 Feb 2006 · 58 references

Pith's verdict: Solid data, unsupported leap: the F1u(1) softening is explained by the paper's own Grüneisen parameter and lattice contraction, with no need for cage expansion.

T0 · AI review

How this review was made: An AI referee (deepseek-v4-flash) read the paper on August 28, 2026 and answered a fixed list of questions about it. T0 is the starting level every paper gets. The levels describe how deeply Pith has checked the paper, never the authors.

T0 AI review An AI read the paper and answered a fixed list of questions.
T1 Audit Automatic checks that the references and files the paper relies on exist and match.
T2 Compute The paper's code or calculations re-run with the same results.
T3 Formal statement The claims written out in a formal math language a computer can read.
T4 Proof Those claims proved, and the proof checked by computer.

How Pith checks papers →

· 5 major objections · 4 minor · Ask about this paper · The compiled record · Read the full review →

Challenge this review Comment (0) Read on arXiv ↗

Cite ▾

arXiv IDcond-mat/0602519 (version 1)

Pith IDKW4GH5SO, Pith's permanent record of this paper and its review

CitationF. Cimpoesu, H. Takagi, J. Cao, J. L. Musfeldt, N. Dragoe, R. J. Cross, S. Brown, S. Ito. "In Search of Microscopic Evidence for Molecular Level Negative Thermal Expansion in Fullerenes." arXiv:cond-mat/0602519 (2006). https://pith.science/paper/KW4GH5SO

Cite this reviewBibTeX for Pith's review of this paper

Claim paper

Why Pith says this

Highlight any text to comment on it.

Editor's note

read the letter

Colleague,

The far-IR measurement is the real contribution: F1u(1) softens by about 0.5 cm^-1 between 300 and 10 K in both C60 and Kr@C60, with two independent runs and error bars. The Kr@C60 comparison is a useful addition, and the literature survey of pressure data is handy.

The interpretation is another story. The paper takes the softening as evidence that the cage expands at low temperature, but their own numbers explain the shift without any cage expansion. Table II gives γ = -0.04 for F1u(1) (from the bulk compressibility and dω/dP), and Table I shows the lattice volume shrinks by about 2.4% between 300 and 5 K. Plug those into Δω/ω = -γΔV/V and you get Δω ≈ -0.5 cm^-1—right on top of the observed softening. So the mode is behaving exactly as expected from the known lattice contraction and a negative Grüneisen parameter. There is no need to invoke molecular-level NTE. The stress-test's sign arithmetic misses this by using α_vib (the cage expansion) in place of the lattice volume; the correct calculation predicts softening, not hardening. But that doesn't rescue the paper—if anything, it makes the standard explanation cleaner.

The EXAFS support is also weak: 3.540(7) vs 3.537(10) Å is within error bars, and the α_vib estimate comes from a small subset of modes with no uncertainty budget.

So the new data are worth reporting, and the softening clearly deserves an explanation. But the claim that this is microscopic evidence for molecular NTE is not supported by the paper's own numbers. A referee should ask the authors to show that the softening exceeds the lattice-contraction baseline before making that leap.

I'd send it to peer review—it's a legitimate experimental contribution that needs a major reinterpretation, not a desk reject. I just wouldn't cite it as evidence for NTE in its current form.

Best

Referee report

Significance

If the interpretation were correct, the paper would provide the first direct microscopic experimental evidence for molecular-level negative thermal expansion in C60, an intriguing result with implications for molecular electronics and for understanding the thermal properties of nanocarbon materials. The study has clear strengths: the new high-resolution far-infrared data on both pristine and endohedral C60 are valuable, the compilation of pressure-dependent mode shifts from the literature is useful, and the explicit comparison with the Kwon et al. prediction structures the analysis. However, the central inference is undermined by an internal sign inconsistency in the Grüneisen analysis and by supporting evidence that is not statistically significant; the quantitative estimate of alpha_vib is also based on an incomplete mode sum. These issues are load-bearing for the paper's main claim.

Major objections (5)

[Results and Discussion, Eq. (2) and Table II] The volume interpretation of the F1u(1) softening is internally inconsistent with the paper's own Grüneisen parameter. Table II lists dω/dP = -1.60 cm-1/GPa and γ = -0.04 for F1u(1). With the definition γ = -∂lnω/∂lnV in Eq. (2), a negative γ implies (∂ω/∂V)_T > 0, so an expanded low-temperature cage would harden this mode rather than soften it. Using the paper's α_vib ≈ -10^-5 K^-1 and ΔT = -290 K, the volume-induced shift is approximately +0.06 cm-1, opposite in sign to the observed -0.5 cm-1 softening. Thus the observed temperature softening cannot be explained by the proposed cage expansion; it would have to be dominated by explicit anharmonicity or crystal-field effects, which the manuscript excludes by attributing both pressure and temperature softening to cage volume effects (footnotes [49] and [55]).
[Results and Discussion, Eq. (1)] The estimate α_vib ≈ -10^-5 K^-1 is not a valid thermal expansion coefficient as presented. Equation (1) is a thermodynamic sum over all phonon modes, whereas Table II includes only a subset of the 46 intramolecular modes, with no acoustic modes and no estimate of the Grüneisen-weighted heat capacity of the omitted modes. The authors acknowledge this limitation in the text, but they nevertheless use the resulting number as a quantitative result and compare it to the EXAFS value. Without bounds on the omitted-mode contributions, the quoted α_vib is not established and cannot be used as support for the NTE claim.
[Independent experimental support (Kr-EXAFS reanalysis)] The EXAFS support is not statistically significant. The paper reports a Kr-C distance of 3.540(7) Å at low temperature and 3.537(10) Å at 300 K; the difference is 0.003 Å with a combined uncertainty of roughly 0.012 Å. This difference is compatible with zero, so the statement that the EXAFS data 'provide broad support' for a relaxed low-temperature cage overstates the evidence. The authors themselves initially characterize the result as indicating a possibility, but later elevate it to independent support without additional analysis.
[Footnote [55] and pressure-temperature equivalence] The mapping between the 0-0.4 GPa pressure regime and the 5 K temperature regime is based only on a match of bulk lattice parameters. This ignores the fact that the pressure and temperature paths cross different orientational phases (fcc to simple cubic at 260 K and to orientationally ordered at 90 K; fcc to simple cubic at 0.4 GPa) and assumes that the bulk lattice constant determines the intramolecular cage volume. Without a microscopic justification, pressure-derived Grüneisen parameters cannot be directly transferred to the temperature dependence of intramolecular modes, and this assumption is load-bearing for the paper's central argument.
[Results and Discussion, Fig. 2 and crystal-field splitting] The F1u(1) mode splits below the 260 K transition (F1u → Au + Eu + 3Fu), as noted in the text, and the manuscript tracks the 'center peak position' of a split multiplet. The apparent 0.5 cm-1 softening could reflect changes in the relative intensities or positions of the crystal-field components rather than a genuine softening of the intrinsic vibrational mode. The paper does not provide a component-resolved fitting analysis for the low-temperature spectra, leaving this alternative explanation unresolved.

Minor objections (4)

[Conclusion] The Conclusion contains a typo: 'We report the the high-resolution...' should read 'We report the high-resolution...'.
[Throughout] The name 'Grüneisen' is misspelled as 'Gr¨ uneissen' in several places (e.g., 'mode Gr¨ uneissen parameters'); the correct spelling should be used consistently.
[Figure 1 caption] The caption states that the blue solid lines correspond to 4 K data, while the text and Fig. 2 describe measurements over the range 300-10 K; this temperature discrepancy should be resolved.
[Methods and Fig. 2] The description of how the 'center peak position' of the F1u(1) mode was determined is insufficient, particularly given the crystal-field splitting at low temperature; a brief description of the fitting model or peak-position extraction would improve reproducibility.

How Pith checks papers → · Full audit of this paper →

The paper

The paper claims

Cooling C60 softens a key vibration, signaling cage expansion

The reading

The paper reports far-infrared measurements of pristine $C_{60}$ and endohedral Kr@$C_{60}$ between 300 and 10 K, focused on the $F_{1u}(1)$ radial vibrational mode at 526 cm$^{-1}$. In both materials this mode softens as temperature falls, whereas ordinary anharmonic behavior would harden it; the authors read this as the fullerene cage becoming more relaxed, that is, larger, at low temperature. Combining their spectra with published pressure- and temperature-dependent Raman, infrared, and krypton EXAFS data, they estimate negative Grüneisen parameters for many intramolecular modes and a vibrational contribution to the thermal expansion coefficient of order $-10^{-5}$ K$^{-1}$. They argue that this molecular-level negative thermal expansion is consistent with a molecular dynamics prediction for $C_{60}$ and should be visible with local probes even though bulk lattice parameters contract normally.

What carries the argument

The load-bearing observable is the frequency of the $F_{1u}(1)$ intramolecular mode near 526 cm$^{-1}$, a largely radial vibration that acts as a local gauge of cage size: a lower frequency signifies a longer, weaker bond and therefore a larger cage. The quantitative engine is the mode Grüneisen parameter, the dimensionless quantity $\gamma_i = -d\ln\omega_i/d\ln V$ that links fractional frequency change to fractional volume change, computed from published pressure derivatives $d\omega_i/dP$ and the isothermal compressibility $\chi_T = 6.9\times 10^{-2}$ GPa$^{-1}$. The authors connect pressure and temperature through the lattice-parameter equivalence that 0 to 0.4 GPa at room temperature corresponds to the 5 K regime, so pressure-induced softening can be read as cooling-induced softening. Weighting the available modes by their heat capacities then yields the pseudo thermal-expansion coefficient $\alpha_{vib}$ on the order of $-10^{-5}$ K$^{-1}$.

Extended reading notes

Core claim

The central claim is that the low-temperature softening of the $F_{1u}(1)$ mode in $C_{60}$ and Kr@$C_{60}$, together with a survey showing several Raman modes softening on cooling and most modes softening under pressure up to 0.4 GPa, is microscopic evidence for negative thermal expansion of the fullerene cage itself. On this view the isolated $C_{60}$ ball is larger at 10 K than at 300 K even though the face-centered cubic lattice parameter decreases with cooling; the cage expansion is a molecular effect, not a bulk one. The authors estimate the vibrational contribution to the thermal expansion coefficient, $\alpha_{vib}$, to be on the order of $-10^{-5}$ K$^{-1}$, and their reanalysis of krypton EXAFS data gives a similar magnitude from the temperature dependence of the Kr-C distance. They therefore frame the result as support for the prediction that small carbon cages exhibit negative thermal expansion driven by structural and vibrational entropic effects.

Load-bearing premise

The argument depends on the assumption that the observed $F_{1u}(1)$ softening on cooling is caused by an expanding fullerene cage rather than by intrinsic anharmonicity, crystal-field symmetry breaking, or sample effects; if the softening is not volume-driven, the Grüneisen estimate and the negative-thermal-expansion conclusion collapse.

Editorial extensions

If this is right

If the cage does expand on cooling, the $C_{60}$ molecule is larger at 10 K than at 300 K even as the crystal lattice shrinks, so local and bulk thermal expansion point in opposite directions.
Negative Grüneisen parameters for many intramolecular modes imply that vibrational entropy favors an expanded cage at low temperature, the mechanism predicted by molecular dynamics.
The effect persists in Kr@$C_{60}$, where the endohedral guest shifts the mode frequency by about 2 cm$^{-1}$, so doping does not destroy the molecular-level negative thermal expansion.
Because the negative contribution is estimated at order $-10^{-5}$ K$^{-1}$, comparable in magnitude to the bulk effect in ZrW$_2$O$_8$ but molecular in origin, bulk measurements can mask it; only local probes such as EXAFS or mode-resolved spectroscopy reveal it.
The same physics may extend to other curved carbon cages and nanotubes, where theoretical predictions remain more controversial.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

If the volume-driven interpretation holds, the high-pressure/low-temperature equivalence used in the paper can be tested directly by measuring the $F_{1u}(1)$ mode in a matrix-isolated or free-standing $C_{60}$ molecule where lattice compression is absent; residual softening would indicate an intrinsic molecular anharmonicity instead of cage expansion.
The opposition between molecular expansion and lattice contraction suggests a design route to zero-thermal-expansion composites: choose a host lattice whose contraction compensates the fullerene cage expansion, yielding a tunable net thermal expansion.
A systematic noble-gas series (He, Ne, Ar, Kr, Xe) inside $C_{60}$ should show a monotonic shift in the observed mode hardening and could map how guest size and polarizability modulate the cage's low-temperature expansion, providing a sharper test of the mechanism.

Original abstract

We report the high-resolution far infrared vibrational properties of C60 and endohedral Kr@C60 fullerene as a function of temperature. Anomalous softening of the F1u(1) mode (526 cm-1) is observed throughout the temperature range of investigation (300 - 10 K) suggesting that the fullerene cage may expand at low temperature in these molecular solids. To test this idea, we combine these results with temperature and pressure dependent Raman, infrared, and Kr extended x-ray absorption fine structure data from the literature to provide a comprehensive view of local cage size effects. The results are consistent with a recent molecular dynamics study [Kwon et al., Phys. Rev. Lett. 92, 15901 (2004)] that predicts negative thermal expansion in carbon fullerenes.

The compiled record

The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.

Compiled by classifier-1.13-20260917 via OpenRouter, question bank abstract-p1-20260923, 2026-09-23: 1 request, 3,786 input tokens, $0.0002 reported.

What the abstract itself states, as probabilities: claims first 0.04 · states limitation 0.18 · human participants 0.01 · controlled comparison 0.11 · randomized assignment 0.01 · states quantitative result 0.78 · compares with prior results 0.95 · mentions code or data availability 0.02.

The abstract, sentence by sentence

arXiv listing abstract v1. Results and the main claim are underlined; show every role.

We report the high-resolution far infrared vibrational properties of C60 and endohedral Kr@C60 fullerene as a function of temperature. Anomalous softening of the F1u(1) mode (526 cm-1) is observed throughout the temperature range of investigation (300 - 10 K) suggesting that the fullerene cage may expand at low temperature in these molecular solids. To test this idea, we combine these results with temperature and pressure dependent Raman, infrared, and Kr extended x-ray absorption fine structure data from the literature to provide a comprehensive view of local cage size effects. The results are consistent with a recent molecular dynamics study [Kwon et al., Phys. Rev. Lett. 92, 15901 (2004)] that predicts negative thermal expansion in carbon fullerenes.

background contribution method result interpretation main claim

What the classifier reports for each sentence. The number is the probability it gave the label.
#	sentence	role	the authors' own work	states the main conclusion	strength
s0	We report the high-resolution far infrared vibrational properties of C60 and endohedral Kr@C60 fullerene as a function of temperature.	contribution 0.99	0.93	0.03	asserted 0.97
s1	Anomalous softening of the F1u(1) mode (526 cm-1) is observed throughout the temperature range of investigation (300 - 10 K) suggesting that the fullerene cage may expand at low temperature in these molecular solids.	result 0.81	0.94	0.55	hedged possibility 0.99
s2	To test this idea, we combine these results with temperature and pressure dependent Raman, infrared, and Kr extended x-ray absorption fine structure data from the literature to provide a comprehensive view of local cage size effects.	method 0.86	0.44	0.04	asserted 0.83
s3	The results are consistent with a recent molecular dynamics study [Kwon et al., Phys. Rev. Lett. 92, 15901 (2004)] that predicts negative thermal expansion in carbon fullerenes.	interpretation 0.91	0.22	0.49	hedged possibility 0.99

What kind of paper the classifier reports this is: empirical study 1.00 · evidence from observation or experiment 0.94.

What was examined, and what was not

sources read

arXiv listing abstract v1

not examined

full text
figures and tables
references and citing sentences
relations to other papers

levels run

P abstract

not run

S sections
T body sentences
C citations
R cross-paper relations

Every quoted sentence on this record is the authors'. Every label is from Pith's closed vocabulary, with the probability shown beside it. Every number in the measurements table is the authors', checked by code. Record as JSON

Figures

**Figure 1.** FIG. 1: (Color online) (a) High resolution far infrared tran

**Figure 2.** FIG. 2: (Color online) Temperature dependence of the center

Figures reproduced from arXiv:cond-mat/0602519 by the authors.

References

Works cited (58)

[49]

All the modes under investigation are intramolecular modes and hence, related to cage rather than lattice ef- fects

View on Pith
[55]

The pressure and temperature dependent behavior of lat - tice parameter clearly shows that the reduction in the lattice constant at 5 K ( ∼ 14.042 ˚A) is already surpassed for pressure larger than 0.41 GPa ( ∼ 14.031 ˚A) at room temperature (Table I). Hence, we correlate the softening of modes up to 0.4 GPa in pressure to the 5 K tempera- ture regime

View on Pith
[1]

J. N. Hancock, C. Turpen, and Z. Schlesinger, G. R. Kowach, A. P. Ramirez, Phys. Rev. Lett. 93, 225501 (2004)

View on Pith 2004
[2]

T. A. Mary, J. S. O. Evans, T. Vogt, and A. W. Sleight, Science 272, 90 (1996)

View on Pith 1996
[3]

G. Ernst, C. Broholm, G. R. Kowach, and A. P. Ramirez, Nature 396, 147 (1998)

View on Pith 1998
[4]

T. R. Ravindran, A. K. Arora, and T. A. Mary, Phys. Rev. Lett. 84, 3879 (2000)

View on Pith 2000
[5]

G. D. Barrera, J. A. O. Bruno, T. H. K. Barron and N. L. Allan, J. Phys.: Condens. Matt. 17, R217 (2005)

View on Pith 2005
[6]

J. B. Nelson, And D. P. Riley, Proc. Phys. Soc. London 57, 477 (1945)

View on Pith 1945
[7]

J. Arvanitidis, K. Papagelis, S. Margadonna, K. Pras- sides, and A. N.Fitch, Nature 425, 599 (2003)

View on Pith 2003
[8]

Y.-K. Kwon, S. Berber, and D. Tom´ anek, Phys. Rev. Lett. 92, 015901 (2004)

View on Pith 2004
[9]

C. Li, and T.-W. Chou, Phys. Rev. B 71, 235414 (2005)

View on Pith 2005
[10]

H. Jiang, B. Liu, Y. Huang, and K. C. Hwang, J. Eng. Mater. Technol. 126, 265 (2004)

View on Pith 2004
[11]

P. K. Schelling, and P. Keblinski, Phys. Rev. B 68, 035425 (2003)

View on Pith 2003
[12]

C. S. Yannoni, P. P. Bernier, D. S. Bethune, G. Meijer, and J. R. Salem, J. Am. Chem. Soc. 113, 3190 (1991)

View on Pith 1991
[13]

R. E. Stanton, and M. D. Newton, J. Phys. Chem. 92, 2141 (1988). 6

View on Pith 1988
[14]

Four infrared active modes are F 1u(1), F 1u(2), F 1u(3) and F 1u(4) at 526, 576, 1182 and 1429 cm − 1 respectively

View on Pith
[15]

P. A. Heiney, G. B. M. Vaughan, J. E. Fischer, N. Cous- tel, D. E. Cox, J. R. D. Copley, D. A. Neumann, W. A. Kamitakahara, K. M. Creegan, D. M. Cox, J. P. Mc- Cauley Jr., and A. B. Smith III, Phys. Rev. B 45, R4544 (1992)

View on Pith 1992
[16]

C. S. Yannoni, R. D. Johnson, G. Meijer, D. S. Bethune, and J. R. Salem, J. Phys. Chem. 95, 9 (1991)

View on Pith 1991
[17]

W. I. F. David, R. M. Ibberson, J. C. Matthewman, K. Prassides, T. J. S. Dennis, J. P. Hare, H. W. Kroto, R. Taylor, and D. R. M. Walton, Nature 353, 147 (1991)

View on Pith 1991
[18]

R. Sachidanandam, and A. B. Harris, Phys. Rev. Lett. 67, 1467 (1991)

View on Pith 1991
[19]

P. A. Heiney, J. E. Fischer, A. R. McGhie, W. J. Ro- manow, A. M. Denenstein, J. P. McCauley Jr., A. B. Smith III, and D. E. Cox, Phys. Rev. Lett. 66, 2911 (1991)

View on Pith 1991
[20]

The lattice parameter increases by 0.044 ± 0.004 ˚A near the 260 K transition [15]

View on Pith
[21]

W. I. F. David, R. M. Ibberson, and T. Matsuo, Proc. R. Soc. London A 442, 129 (1993)

View on Pith 1993
[22]

S. Z. Liu, Y.-J. Lu, M. M. Kappes, and J. A. Ibers, Sci- ence 254, 408 (1991)

View on Pith 1991
[23]

A. P. Jephcoat, J. A. Hriljac, L. W. Finger, and D. E. Cox, Europhys. Lett. 25, 429 (1994)

View on Pith 1994
[24]

H. M. Lee, M. M. Olmstead, T. Suetsuna, H. Shimotani, N. Dragoe, R. J. Cross, K. Kitazawa, and A. L. Balch, Chem. Commun. 13, 1352 (2002)

View on Pith 2002
[25]

S. Ito, A. Takeda, T. Miyazaki, Y. Yokoyama, M. Saun- ders, R. J. Cross, H. Takagi, P. Berthet, and N. Dragoe, J. Phys. Chem. B 108, 3191 (2004)

View on Pith 2004
[26]

A. Takeda, Y. Yokoyama, S. Ito, T. Miyazaki, H. Shi- motani, K. Yakigaya, T. Kakiuchi, H. Sawa, H. Takagi, K. Kitazawa, and N. Dragoe, Chem. Comm. (In Press)

View on Pith
[27]

P. H. M. van Loosdrecht, P. J. M. van Bentum, and G. Meijer, Phys. Rev. Lett. 68, 1176 (1992)

View on Pith 1992
[28]

M. Matus, and H. Kuzmany, Appl. Phys. A 56, 241 (1993)

View on Pith 1993
[29]

Y. Hamanaka, M. Norimota, S. Nakashima, and M. Hangyo, J. Phys.: Condens. Matt. 7, 9913 (1995)

View on Pith 1995
[30]

P. J. Horoyski, M. L. W. Thewalt, and T. R. Anthony, Phys. Rev. Lett. 74, 194 (1995)

View on Pith 1995
[31]

K. P. Meletov, D. Christoﬁlos, S. Ves, and G. A. Kourouklis, Phys. Rev. B 52, 10090 (1995)

View on Pith 1995
[32]

N. Chandrabhas, M. N. Shashikala, D. V. S. Muthu, A. K. Sood, and C. N. R. Rao, Chem. Phys. Lett. 197, 319 (1992)

View on Pith 1992
[33]

D. W. Snoke, Y. S. Raptis, and K. Syassen, Phys. Rev. B 45, R14419 (1992)

View on Pith 1992
[34]

K. Aoki, H. Yamawaki, Y. Kakudate, M. Yoshida, S. Usuba, H. Yokoi, S. Fujiwara, Y. Bae, R. Malhotra, and D. Lorents, J. Phys. Chem. 95, 9037 (1991)

View on Pith 1991
[35]

M. C. Martin, X. Du, J. Kwon, and L. Mihaly, Phys. Rev. B 50, R173 (1994)

View on Pith 1994
[36]

K. P. Meletov, G. A. Kourouklis, D. Christoﬁlos, and S. Ves, JETP 81, 798 (1995)

View on Pith 1995
[37]

Y. Huang, D. F. R. Gilson, and I. S. Butler, J. Phys. Chem. 95, 5723 (1991)

View on Pith 1991
[38]

C. C. Homes, P. J. Horoyski, M. L. W. Thewalt, and B. P. Clayman, Phys. Rev. B 49, R7052 (1994)

View on Pith 1994
[39]

The low temperature space group is Pa ¯3

View on Pith
[40]

The natural abundance of 13C reduces symmetry even further [41]

View on Pith
[41]

Z.-H. Dong, P. Zhou, J. M. Holden, P. C. Eklund, M. S. Dresselhaus, G. Dresselhaus, Phys. Rev. B 48, R2862 (1993)

View on Pith 1993
[42]

L. R. Narasimhan, D. N. Stoneback, A. F. Hebard, R. C. Haddon, and C. K. N. Patel, Phys. Rev. B 46, 2591 (1992)

View on Pith 1992
[43]

Additional modes (291, 437, 602 cm − 1) also appear in the infrared response of Kr@C 60

View on Pith
[44]

K. Yamamoto, M. Saunders, A. Khong, R. J. Cross, M. Grayson, M. L. Gross, A. F. Benedetto, and R. B. Weis- man, J. Am. Chem. Soc. 121, 1591 (1999)

View on Pith 1999
[45]

Y. Yokoyama, S. Ito, A. Takeda, T. Miyazaki, H. Shi- motani, F. Cimpoesu, N. Dragoe, H. Takagi and K. Ki- tazawa, Unpublished results

View on Pith
[46]

Both studies argued that the longer wavelength excita- tion eliminates problems related to sample heating and photo-degradation [29, 30]

View on Pith
[47]

R. ´Swietlik, K. Yakushi, K. Yamamoto, T. Kawamoto, and T. Mori, Journal of Molecular Structure 704, 89 (2004)

View on Pith 2004
[48]

H. H. Wang, J. R. Ferraro, J. M. Williams, U. Geiser, and J. A. Schlueter, J. Chem. Soc.-Chem. Commun. 16, 1893 (1994)

View on Pith 1994
[50]

T. H. K. Barron, and G. K. White, Heat Capacity and Thermal Expansion at Low Temperatures (Kluwer Aca- demic/Plenum Publishers, New York, 1999)

View on Pith 1999
[51]

The intermediate region could not be measured as it has a strong Raman mode of diamond at 1333.4 cm − 1 which is many orders of magnitude stronger than the Raman modes of C 60

View on Pith
[52]

Aoki et al. proposed that the eﬀect in the F 1u mode might be due a covalent-bond-like interaction formed between contacting faces of the adjacent molecules [34] and sug- gested that these intermolecular attractive force (along the radial axes) can be strengthened through the increase in the π orbital overlapping as the molecules approach each other under...

View on Pith
[53]

B. Sundqvist, Advances in Physics, 48, 1 (1999)

View on Pith 1999
[54]

J. E. Fischer, P. A. Heiney, A. R. McGhie, W. J. Ro- manow, A. M. Denenstein, J. P. McCauley, and A. B. Smith, Science 252, 1288 (1991)

View on Pith 1991
[56]

K. Allen, and F. Hellman, Phys. Rev. B 60, 11765 (1999)

View on Pith 1999
[57]

F. Gompf, B. Renker, H. Schober, P. Adelmann, and R. Heid, J. Supercond. 7, 643 (1994)

View on Pith 1994
[58]

Note that the size of error bar is mainly due to ﬁtting procedure. Examination of the data (inset in Fig. 1(b)) clearly shows that the peak of the radial distribution function is at a higher value of R at low temperature (77 K)

View on Pith

Discussion

Disagree with the review, or know something it missed? Leave a comment, highlight any passage above to comment on it, or challenge this review formally.

[1] [49]

All the modes under investigation are intramolecular modes and hence, related to cage rather than lattice ef- fects

View on Pith

[2] [55]

The pressure and temperature dependent behavior of lat - tice parameter clearly shows that the reduction in the lattice constant at 5 K ( ∼ 14.042 ˚A) is already surpassed for pressure larger than 0.41 GPa ( ∼ 14.031 ˚A) at room temperature (Table I). Hence, we correlate the softening of modes up to 0.4 GPa in pressure to the 5 K tempera- ture regime

View on Pith

[3] [1]

J. N. Hancock, C. Turpen, and Z. Schlesinger, G. R. Kowach, A. P. Ramirez, Phys. Rev. Lett. 93, 225501 (2004)

View on Pith 2004

[4] [2]

T. A. Mary, J. S. O. Evans, T. Vogt, and A. W. Sleight, Science 272, 90 (1996)

View on Pith 1996

[5] [3]

G. Ernst, C. Broholm, G. R. Kowach, and A. P. Ramirez, Nature 396, 147 (1998)

View on Pith 1998

[6] [4]

T. R. Ravindran, A. K. Arora, and T. A. Mary, Phys. Rev. Lett. 84, 3879 (2000)

View on Pith 2000

[7] [5]

G. D. Barrera, J. A. O. Bruno, T. H. K. Barron and N. L. Allan, J. Phys.: Condens. Matt. 17, R217 (2005)

View on Pith 2005

[8] [6]

J. B. Nelson, And D. P. Riley, Proc. Phys. Soc. London 57, 477 (1945)

View on Pith 1945

[9] [7]

J. Arvanitidis, K. Papagelis, S. Margadonna, K. Pras- sides, and A. N.Fitch, Nature 425, 599 (2003)

View on Pith 2003

[10] [8]

Y.-K. Kwon, S. Berber, and D. Tom´ anek, Phys. Rev. Lett. 92, 015901 (2004)

View on Pith 2004

[11] [9]

C. Li, and T.-W. Chou, Phys. Rev. B 71, 235414 (2005)

View on Pith 2005

[12] [10]

H. Jiang, B. Liu, Y. Huang, and K. C. Hwang, J. Eng. Mater. Technol. 126, 265 (2004)

View on Pith 2004

[13] [11]

P. K. Schelling, and P. Keblinski, Phys. Rev. B 68, 035425 (2003)

View on Pith 2003

[14] [12]

C. S. Yannoni, P. P. Bernier, D. S. Bethune, G. Meijer, and J. R. Salem, J. Am. Chem. Soc. 113, 3190 (1991)

View on Pith 1991

[15] [13]

R. E. Stanton, and M. D. Newton, J. Phys. Chem. 92, 2141 (1988). 6

View on Pith 1988

[16] [14]

Four infrared active modes are F 1u(1), F 1u(2), F 1u(3) and F 1u(4) at 526, 576, 1182 and 1429 cm − 1 respectively

View on Pith

[17] [15]

P. A. Heiney, G. B. M. Vaughan, J. E. Fischer, N. Cous- tel, D. E. Cox, J. R. D. Copley, D. A. Neumann, W. A. Kamitakahara, K. M. Creegan, D. M. Cox, J. P. Mc- Cauley Jr., and A. B. Smith III, Phys. Rev. B 45, R4544 (1992)

View on Pith 1992

[18] [16]

C. S. Yannoni, R. D. Johnson, G. Meijer, D. S. Bethune, and J. R. Salem, J. Phys. Chem. 95, 9 (1991)

View on Pith 1991

[19] [17]

W. I. F. David, R. M. Ibberson, J. C. Matthewman, K. Prassides, T. J. S. Dennis, J. P. Hare, H. W. Kroto, R. Taylor, and D. R. M. Walton, Nature 353, 147 (1991)

View on Pith 1991

[20] [18]

R. Sachidanandam, and A. B. Harris, Phys. Rev. Lett. 67, 1467 (1991)

View on Pith 1991

[21] [19]

P. A. Heiney, J. E. Fischer, A. R. McGhie, W. J. Ro- manow, A. M. Denenstein, J. P. McCauley Jr., A. B. Smith III, and D. E. Cox, Phys. Rev. Lett. 66, 2911 (1991)

View on Pith 1991

[22] [20]

The lattice parameter increases by 0.044 ± 0.004 ˚A near the 260 K transition [15]

View on Pith

[23] [21]

W. I. F. David, R. M. Ibberson, and T. Matsuo, Proc. R. Soc. London A 442, 129 (1993)

View on Pith 1993

[24] [22]

S. Z. Liu, Y.-J. Lu, M. M. Kappes, and J. A. Ibers, Sci- ence 254, 408 (1991)

View on Pith 1991

[25] [23]

A. P. Jephcoat, J. A. Hriljac, L. W. Finger, and D. E. Cox, Europhys. Lett. 25, 429 (1994)

View on Pith 1994

[26] [24]

H. M. Lee, M. M. Olmstead, T. Suetsuna, H. Shimotani, N. Dragoe, R. J. Cross, K. Kitazawa, and A. L. Balch, Chem. Commun. 13, 1352 (2002)

View on Pith 2002

[27] [25]

S. Ito, A. Takeda, T. Miyazaki, Y. Yokoyama, M. Saun- ders, R. J. Cross, H. Takagi, P. Berthet, and N. Dragoe, J. Phys. Chem. B 108, 3191 (2004)

View on Pith 2004

[28] [26]

A. Takeda, Y. Yokoyama, S. Ito, T. Miyazaki, H. Shi- motani, K. Yakigaya, T. Kakiuchi, H. Sawa, H. Takagi, K. Kitazawa, and N. Dragoe, Chem. Comm. (In Press)

View on Pith

[29] [27]

P. H. M. van Loosdrecht, P. J. M. van Bentum, and G. Meijer, Phys. Rev. Lett. 68, 1176 (1992)

View on Pith 1992

[30] [28]

M. Matus, and H. Kuzmany, Appl. Phys. A 56, 241 (1993)

View on Pith 1993

[31] [29]

Y. Hamanaka, M. Norimota, S. Nakashima, and M. Hangyo, J. Phys.: Condens. Matt. 7, 9913 (1995)

View on Pith 1995

[32] [30]

P. J. Horoyski, M. L. W. Thewalt, and T. R. Anthony, Phys. Rev. Lett. 74, 194 (1995)

View on Pith 1995

[33] [31]

K. P. Meletov, D. Christoﬁlos, S. Ves, and G. A. Kourouklis, Phys. Rev. B 52, 10090 (1995)

View on Pith 1995

[34] [32]

N. Chandrabhas, M. N. Shashikala, D. V. S. Muthu, A. K. Sood, and C. N. R. Rao, Chem. Phys. Lett. 197, 319 (1992)

View on Pith 1992

[35] [33]

D. W. Snoke, Y. S. Raptis, and K. Syassen, Phys. Rev. B 45, R14419 (1992)

View on Pith 1992

[36] [34]

K. Aoki, H. Yamawaki, Y. Kakudate, M. Yoshida, S. Usuba, H. Yokoi, S. Fujiwara, Y. Bae, R. Malhotra, and D. Lorents, J. Phys. Chem. 95, 9037 (1991)

View on Pith 1991

[37] [35]

M. C. Martin, X. Du, J. Kwon, and L. Mihaly, Phys. Rev. B 50, R173 (1994)

View on Pith 1994

[38] [36]

K. P. Meletov, G. A. Kourouklis, D. Christoﬁlos, and S. Ves, JETP 81, 798 (1995)

View on Pith 1995

[39] [37]

Y. Huang, D. F. R. Gilson, and I. S. Butler, J. Phys. Chem. 95, 5723 (1991)

View on Pith 1991

[40] [38]

C. C. Homes, P. J. Horoyski, M. L. W. Thewalt, and B. P. Clayman, Phys. Rev. B 49, R7052 (1994)

View on Pith 1994

[41] [39]

The low temperature space group is Pa ¯3

View on Pith

[42] [40]

The natural abundance of 13C reduces symmetry even further [41]

View on Pith

[43] [41]

Z.-H. Dong, P. Zhou, J. M. Holden, P. C. Eklund, M. S. Dresselhaus, G. Dresselhaus, Phys. Rev. B 48, R2862 (1993)

View on Pith 1993

[44] [42]

L. R. Narasimhan, D. N. Stoneback, A. F. Hebard, R. C. Haddon, and C. K. N. Patel, Phys. Rev. B 46, 2591 (1992)

View on Pith 1992

[45] [43]

Additional modes (291, 437, 602 cm − 1) also appear in the infrared response of Kr@C 60

View on Pith

[46] [44]

K. Yamamoto, M. Saunders, A. Khong, R. J. Cross, M. Grayson, M. L. Gross, A. F. Benedetto, and R. B. Weis- man, J. Am. Chem. Soc. 121, 1591 (1999)

View on Pith 1999

[47] [45]

Y. Yokoyama, S. Ito, A. Takeda, T. Miyazaki, H. Shi- motani, F. Cimpoesu, N. Dragoe, H. Takagi and K. Ki- tazawa, Unpublished results

View on Pith

[48] [46]

Both studies argued that the longer wavelength excita- tion eliminates problems related to sample heating and photo-degradation [29, 30]

View on Pith

[49] [47]

R. ´Swietlik, K. Yakushi, K. Yamamoto, T. Kawamoto, and T. Mori, Journal of Molecular Structure 704, 89 (2004)

View on Pith 2004

[50] [48]

H. H. Wang, J. R. Ferraro, J. M. Williams, U. Geiser, and J. A. Schlueter, J. Chem. Soc.-Chem. Commun. 16, 1893 (1994)

View on Pith 1994

[51] [50]

T. H. K. Barron, and G. K. White, Heat Capacity and Thermal Expansion at Low Temperatures (Kluwer Aca- demic/Plenum Publishers, New York, 1999)

View on Pith 1999

[52] [51]

The intermediate region could not be measured as it has a strong Raman mode of diamond at 1333.4 cm − 1 which is many orders of magnitude stronger than the Raman modes of C 60

View on Pith

[53] [52]

Aoki et al. proposed that the eﬀect in the F 1u mode might be due a covalent-bond-like interaction formed between contacting faces of the adjacent molecules [34] and sug- gested that these intermolecular attractive force (along the radial axes) can be strengthened through the increase in the π orbital overlapping as the molecules approach each other under...

View on Pith

[54] [53]

B. Sundqvist, Advances in Physics, 48, 1 (1999)

View on Pith 1999

[55] [54]

J. E. Fischer, P. A. Heiney, A. R. McGhie, W. J. Ro- manow, A. M. Denenstein, J. P. McCauley, and A. B. Smith, Science 252, 1288 (1991)

View on Pith 1991

[56] [56]

K. Allen, and F. Hellman, Phys. Rev. B 60, 11765 (1999)

View on Pith 1999

[57] [57]

F. Gompf, B. Renker, H. Schober, P. Adelmann, and R. Heid, J. Supercond. 7, 643 (1994)

View on Pith 1994

[58] [58]

Note that the size of error bar is mainly due to ﬁtting procedure. Examination of the data (inset in Fig. 1(b)) clearly shows that the peak of the radial distribution function is at a higher value of R at low temperature (77 K)

View on Pith